sdspi: fix compatibility issue in multi block read

sdspi: fix compatibility issue in multi block read

SDSPI driver optimized polling of the response tokens by requesting
two extra bytes on top of the block size (512) and CRC (2), and
checking whether these bytes contained the data response token or
not. In case the token was there, further polling would not need to
happen, thereby reducing latency between two consecutive blocks
transferred. However this caused compatibility issues when these two
extra bytes were sent after reading the final block. When
STOP_TRANSMISSION command was sent, these extra two bytes were
treated as part of the command, causing an invalid command error.

This fixes the logic by only requesting extra two bytes if the block
being read is not the final block. In addition to that, more strict
error checking is implemented for command response tokens.